Impaired routing of wild type FXYD2 after oligomerisation with FXYD2-G41R might explain the dominant nature of renal hypomagnesemia

Abstract

Autosomal dominant renal hypomagnesemia, associated with hypocalciurea, has been linked to a G to A mutation at nucleotide position 121 in the FXYD2 gene, resulting in the substitution of Gly with Arg at residue 41 of the protein. FXYD2, also called the Na,K-ATPase gamma-subunit, binds to Na,K-ATPase and influences its cation affinities. In this paper, we provide evidence for the molecular mechanism underlying the dominant character of the disorder. Co-immunoprecipitation experiments using tagged FXYD2 proteins demonstrated that wild type FXYD2 proteins oligomerise. Moreover, FXYD2-G41R also shows oligomerisation with itself and with the wild type protein. In the case of FXYD2-G41R, however, formation of homo-oligomers was prevented by addition of DTT or introduction of the C52A mutation. Finally, we demonstrated that artificial glycosylation of the wild type FXYD2 is reduced when co-expressed with FXYD2-G41R. These data indicate that binding of FXYD2-G41R to wild type FXYD2 subunit might abrogate the routing of wild type FXYD2 to the plasma membrane thus causing the dominant nature of this mutation.

Magnesium in Man: Implications for Health and Disease

“…Urinary Mg 2ϩ excretion was increased, whereas Ca 2ϩ excretion was slightly lowered (172). The c.G121A mutation results in a p.G41R missense mutation at the protein level, which causes misrouting of FXYD2 to the membrane (66). FXYD2 encodes for the ␥-subunit of the Na ϩ -K ϩ -ATPase.…”

Distal Convoluted Tubule

“…In isolated dominant hypomagnesemia, mutations in the small g-subunit of the Na 1 -K 1 -ATPase, FXYD2, alter pump function (111)(112)(113). Specifically, the absence of this subunit, which is highly expressed in the thick ascending limb of Henle's loop and DCT, has been shown to alter the affinity of the Na 1 -K 1 -ATPase for sodium and potassium (114,115).…”

Molecular Determinants of Magnesium Homeostasis

“…Expression with the other subunits alters the kinetics of the pump such that it has an increased affinity for K ϩ at negative membrane potentials, 77,82 a decreased affinity for Na ϩ , 77,83 and altered affinity for ATP. 84 Coexpression of the mutant subunit with wild-type protein prevented trafficking to the plasma membrane, 76,85 although association between wild-type and mutant subunits is not observed with synthetic peptides. 86 Regardless, decreased or absent ␥-subunits affect pump activity and consequently alter intracellular K ϩ concentration.…”